1. Field of the Invention
Electroplated chromium, as a surface material, has many advantages. It is hard and corrosion resistant, has a low coefficient of friction and is a good conductor of heat and electricity. Accordingly, it is greatly used as a surface material in the manufacture of new and in the repair of worn industrial equipment for purposes of extended life, greatly improved performance or in the economical salvaging to size of worn components. However, where electrodeposited chromium is involved in a use which involves friction and where lubrication is a requirement and especially in those areas operating under boundary lubrication conditions, an electroplated chromium surface with none or an insufficient amount of porosity, tends to gall or seize due to its inability to wet or to retain sufficient lubrication; on the other hand, if percentage or degree of porosity is too excessive or if the bearing plateau sizes are too small, lubricant can be wasted or mating parts may wear excessively. Internal combustion cylinders and liners, compressors, pistons, piston rods, piston rings and similar type industrial equipment are prime examples of equipment requiring porosity in a chrome surface. In addition to the requirement of a porous chrome surface, it is desirable and advantageous to have a certain degree or percentage of non-connected type pits of a specific geometry, to retain lubricant and lubricate a surface uniformly without excessive waste as is generally the case with a deep network type porous chromium.
2. Description of the Prior Art
U.S. Pat. Nos. 2,314,604, 2,412,698, 2,755,242 and 2,947,674, all describe treatment of chromium surfaces to provide a porous wear-resistant chromium surface. Other methods involve substrate roughening by pressure grit blasting or selective machining before chromium plating followed by subsequent limited honing, polishing or grinding to provide a porous chrome surface. Another method is to diamond hone a surface and use as is or followed by fine abrasive blasting or finally honing the rough diamond produced surface with a suitable stone to produce pits and plateau bearing surfaces. Another method is to hone or grind a chromium surface to size, followed by D.C. reversing with the product used as is or further treated by light honing to produce a porous chrome surface, which consists of a connected type network of cracks.
The text, Chromium Plating, by Morisset, et al., Robert Draper Ltd., Middlesex, England, 1954, describes the nature of the chromium surface and its treatment, pages 123-129.